iMac - iMac: Won't get passed white screen

Earilaer today I was on my computers desktop gong into my Applications folder when my computer froze. Nothing worked at all so I held down the power button until it turned off. I then waited about 5 or so minutes to turn it back on. I turned it on and I got to the greyish screen and the apple logo came up. During this time the fan was loud and on but turned off. Usually it stays on for about 30 seconds after I get to my desktop. I turned it off again the same way as before but this time I turned it on and the computer got only to the very first white screen. The fan did the same thing as before and nothing else happened. There is a disk in my drive, I think its some type of old game or a CD so I can't put my start up disk in there. I tried holding down my mouse when I start the computer to get the disk out but nothing happened. Im not sure what to do. I don't have Applecare.

So does anyone have any ideas as to what I should try?

My iMac is a 24" Intel Mid 2007.

I apologise in advance if there is already a thread on this. I serched but came up short.

1. hold the power down for 10 seconds
2. power back on while holding down P, R, CMD, and ALT until you hear the second apple chime sound

if that doesn't work then

From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
Unplug all cables from the computer, including the power cord and any display cables.
Wait at least 15 seconds.
Plug the power cord back in, making sure the power button is not being pressed at the time. Then reconnect your keyboard and mouse to the computer.
Press the power button on the back to start up your computer.

I have just tried all of that but still nothing happens. I did do the SMc reset and when I turned it on it went to the white screen and then the grey screen slowly came down. Once that was down the apple logo came up but right after that I got the message in a few different languages that tells me to restart the computer. Once I did that it just went back to only getting to the white screen.

Im thinking I might take it to the Genuis Bar thing at the local apple store. Would that be the best idea to do?

Earilaer today I was on my computers desktop gong into my Applications folder when my computer froze. Nothing worked at all so I held down the power button until it turned off. I then waited about 5 or so minutes to turn it back on. I turned it on and I got to the greyish screen and the apple logo came up. During this time the fan was loud and on but turned off. Usually it stays on for about 30 seconds after I get to my desktop. I turned it off again the same way as before but this time I turned it on and the computer got only to the very first white screen. The fan did the same thing as before and nothing else happened. There is a disk in my drive, I think its some type of old game or a CD so I can't put my start up disk in there. I tried holding down my mouse when I start the computer to get the disk out but nothing happened. Im not sure what to do. I don't have Applecare.

So does anyone have any ideas as to what I should try?

My iMac is a 24" Intel Mid 2007.

I apologise in advance if there is already a thread on this. I serched but came up short.

Thank you everyone for your help!

Okay, so that was loong time ago, but for people who have this problem NOW, there you go.

So, iv got the same problem, but apple store is way to far, and i don't have my license yet, so iv tried to do everything i could, and have made my computer work again.
I have 27'' iMac,3.2GHz, intel core i3, 2010. I had a boot camp windows installed on it, witch was working with no problems, so at least I could copy all of my files to external hard drive. But the fact that i had my windows work perfectly, i knew that the problem that i (we) had is not with hardware.

There is 2 DVD, that have came with my computer: one is Mac OS X install DVD, and the second one is iMac application install DVD. I have inserted the first one into my computer, and booted it of the DVD. (to boot from dvd drive, turn off your computer any way you want, then turn it back on and press opton(alt) key starting as son as you hear the apple-turn-on sound, and keep pressing it until you will see the picture of your hard drive, and then, you can press the "eject the CD/DVD" key on your keyboard. The current CD/DVD will be ejected, and you can put in the iMac OS X install DVD. Than you should wait at least a minute, you will see a new CD pic. on there, chose it and press "enter".)
After booting my computer of that DVD, you will see that grayish screen but this time wait. ( the information is loading from the DVD. It will take about 2-5 minutes, but you should wait all 10. If it doesn't work, start over with that booting thing), it will tell you, that its gonna install you a new OS, but don't worry about that. In the menu you'll see, you will have to chose a language, so do it. After that, you will see a regular Mac top screen bar, with something like """apple sign", "mac OS installer", bla bla bla... , and finally "utilities"" on it. We need the utilities thing. Click it, and it will give you different utilities. The one that i have used,(and probably you should) is "Disk utility". Open it, and choose the hard drive with the installed Mac OS on it (probably it will be named Macintosh HD. Then, click the "verify disk", it should take some time, and after its done (hopefully saying that you have tons of errors and problems with it), click "Repair Disk".Hopefully it will repair it. Then you can run the "verify the disk permissions" test, and then "repair disk permissions".
That the thing that have SAVED my iMac. So now just shut it down by pressing the power button, and turn it on as regular, and it MUST work!!!!

If it doesn't, you van run some other tests, (for example a hardware test that is on the other DVD, just boot for it). But if it DOES work, well… we are happy people now, with working Macs .
i am very new to the mac, and i am very happy (and proud) that i have solved this problem, zoo please email me, if it worked for you!! nk.ddrozd@gmial.com, or to my mailbox on mac-forums.com